The present invention relates to powered conveyors suitable for use in a cleanroom, especially conveyors with slippable rollers used in a class 1 cleanroom.
In order to bring down the cost of various electronic components such as hard disks and integrated circuits, it is often necessary to automate the handling of these components during manufacturing. Since a large portion of the manufacturing costs of these components are incurred in cleanrooms, the automation of material handling within the cleanroom can significantly reduce the cost of the component.
One significant way to automate material handling in a cleanroom is by use of a powered conveyor with slippable rollers. Conveyors with slippable rollers have long been considered an especially good way to move material, especially material that must be handled smoothly. The slippable rollers of such conveyors provide a driving force that is proportional to the weight of the object being conveyed, yet do not slide against the surface of the object being conveyed if its motion is impeded. Instead, slippage occurs at the interface of the slippable roller and the roller shaft.
However, such conveyors may not be useful in a class 1 cleanroom because of the particulate matter that they may add to the cleanroom. For example, the slippable interface between the roller shaft and the slippable roller may generate particulate matter, a situation which is exacerbated on those conveyors having large numbers of rollers on each roller shaft.
Further, the motor drive and roller shaft driving mechanisms may also generate particulate matter which escapes into the cleanroom. Likewise, a lift and transfer mechanism with rubbing surfaces may also generate particulate matter which escapes into the cleanroom.
Further, many conveyors are not configured for the internal aerodynamics of a class 1 cleanroom. Such cleanrooms typically have a source of clean air in the ceiling, and an evacuator for room air in the floor, resulting in a generally downward flow of air. It is important that the air flow generally downward and not laterally, and also laminarly and not turbulently. However, many conveyors are not compatible with these considerations. For example, those conveyors with numerous rollers on each roller shaft may obstruct a large portion of the flow area of the conveying surface, and thus prevent the smooth, downward flow of air past the rollers and roller shafts. Sometimes the motor and electrical component cabinets of the conveyor protrude excessively beneath the surface path of the conveyor, and thus disrupt the downward flow of air. Further, the sides of many conveyors are open, thus permitting excessive lateral flow of air. Some conveyors includes components with excessive horizontal surface areas, on which particulate matter may settle rather than being evacuated from the room. These horizontal surfaces and other external surfaces are sometimes equipped with protrusions that prevent easy cleaning of the surfaces by maintenance personnel.
What is needed is an apparatus that overcomes these disadvantages. The present invention does this in a novel and unobvious way.